Republican Gov. Jack Dalrymple signed into law a measure that outlaws abortions after 20 weeks of pregnancy based on the disputed premise that at that point a fetus can feel pain.

The law signed Tuesday is the latest among a raft of measures passed in North Dakota this session that are meant to challenge the U.S. Supreme Court's 1973 Roe v. Wade ruling that legalized abortion up until viability, usually at 22 to 24 weeks.

Abortion-rights advocates have called the laws blatantly unconstitutional and have promised a long legal fight that they say the state can't win.

Dalrymple last month signed a law that bans abortion as early as six weeks, or when a fetal heartbeat is detected, making North Dakota the most restrictive state in the U.S. in which to get the procedure.

Dalrymple also signed into law last month other measures that make the state the first to ban abortions based on genetic defects such as Down syndrome and require a doctor who performs abortions to be a physician with hospital-admitting privileges. The measures also ban abortion based on genetic selection.

Abortion-rights activists say the signed measures, which take effect Aug. 1, are aimed at closing North Dakota's sole abortion clinic, the Red River Women's Clinic in downtown Fargo.

At least 10 states have passed bills banning abortions after 20 weeks of pregnancy on the premise that a fetus can feel pain at that stage, but research is split on the theory.

North Dakota lawmakers also moved last month to seek a referendum measure defining life as starting at conception, essentially banning abortion in the state. The measure is likely to come before voters in November 2014.

The Center for Reproductive Rights has said it is committed to challenging the fetal heartbeat bill on behalf of the Fargo clinic.

The New York-based group is representing the clinic for free in a trail that started Tuesday over a 2011 law banning the widely accepted use of a medication that induces abortion. A judge has temporarily blocked enforcement of that law.

The Center for Abortion Rights also was part of a lawsuit filed Tuesday that seeks to overturn the more restrictive of the southern state's two new abortion laws, saying the near-ban of abortions from the 12th week of pregnancy onward is unconstitutional.

The group joined with the American Civil Liberties Union of Arkansas to file the lawsuit on behalf of two doctors who provide abortions at a Little Rock clinic. The lawsuit says Arkansas' ban clearly contradicts the standard of viability established by the U.S. Supreme Court's Roe v. Wade decision.

"We are asking the court to block an attempt to essentially outlaw all abortions past 12 weeks, so early that a woman might not know the complete health and status of her pregnancy," Rita Sklar, executive director of Arkansas' ACLU chapter, said at a news conference.

The lawsuit contends that the two doctors could lose their licenses if they provide abortions starting at the 12th week of pregnancy, meaning the law denies "patients their constitutionally-guaranteed right to decide to end a pre-viability pregnancy." It names members of the State Medical Board as defendants because the board is responsible for licensing medical professionals.

Arkansas' 12-week ban is tied to the date at which a fetal heartbeat can typically be detected by an abdominal ultrasound. The ban includes exemptions for rape, incest, the life of the mother and highly lethal fetal disorders.

Rose Mimms, the executive director of Arkansas Right to Life, said anti-abortion groups like hers are hopeful that the new abortion restrictions being passed in conservative-leaning states will land before the U.S. Supreme Court and be considered against new discoveries regarding fetal development.

"They didn't have that kind of information when they decided Roe v. Wade," Mimms said, referring to the 1973 decision that legalized abortion until a fetus could viably survive outside the womb. A fetus is generally considered viable at 22 to 24 weeks.

The 12-week ban is scheduled to take effect 90 days after the Legislature formally adjourns, which is expected to happen next month.

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Associated Press writer Jeannie Nuss in Little Rock, Arkansas, contributed to this report.